The present invention generally relates to vascular support garments. More specifically, the present invention relates to counterpressure garments that can be used in low pressure environments such as outer space.
In environments having very small or no ambient gas pressure, such as high altitude or the vacuum of space, a subject's respiration and circulatory balance are of concern. Gas needs to be delivered to the subject's lungs at a high enough pressure to cause diffusion of oxygen into the blood. It has been found that a gas pressure of about 222 mm Hg is minimally needed for proper breathing.
As pressure of the breathing gas rises, blood pressure similarly rises. But tissue pressure that substantially matches the blood pressure must exist. Otherwise, the circulating blood can rush into low pressure areas and pool. If tissue pressure is not sufficiently high, the veins (and particularly the small ones) will become engorged with blood. As venous engorgement continues, pressure within the veins and capillaries continues to increase. If the pressure exceeds about 10 mm Hg, measurable amounts of excess fluid can be forced through the capillary walls and accumulate in the tissues. The accumulation of fluid can result in edema and a decrease in the circulating blood volume.
To provide adequate pressure in the tissue to prevent pooling, various suits have been employed to provide a counterpressure on the tissue. Typically, these suits have used an inelastic and tightly fitted outer garment. The inelastic outer garment oftentimes covers bladders that apply constant counterpressure to the body. Also incorporated in the inelastic garment have been tubes running over the limbs and trunk. The tubes inflate, either from being gas filled or simply as the ambient pressure is decreased, pulling the suit material tight and thereby applying counterpressure to the body.
A different type of space suit is a "full pressure suit." It is a body-shaped garment that is gas tight and filled with oxygen under pressure so that the lungs and skin are pressurized equally. There is no circulatory imbalance.
While addressing some of the physiological concerns, the gas filled pressure suits have posed various problems. The inflated suit is rigid, except where special joint structures are added, and not all natural motions are thus possible. There is a relatively high energy cost of activity. Body temperature regulation due to the impermeability of the suit necessitates elaborate cooling systems. And with the need for pressurized gas within the suit, a danger associated with rupturing or tears exists. In the glove part of the suit, the gas causes the glove to balloon over the hand and severely limits dexterity.
In part to minimize the disadvantages associated with high energy cost and restricted mobility in gas filled suits, a space activity suit (SAS) was developed with elastic cloth material which itself provided countepressure to the body. No special joints are needed since the elastic cloth bends easily. The SAS also allowed direct evaporation of sweat in the absence of the type of cooling system associated with a gas filled suit. The SAS has also tended to be more flexible and less bulky than the gas filled suit, thereby increasing mobility.
Notwithstanding its advantages, the SAS still has drawbacks. For example, if a counterpressure is to be evenly applied around a circumference, a body part must be perfectly circular. But the body is not circular, and is instead ovate, ellipsoidal and irregular. Areas of the body which are far from circular include the hands, which have a concave palm and a convex dorsum. In the specific context of the hand, the elastic material tends to primarily press at the outer edge of the hand and, accordingly leave the dorsum and palm without significant counterpressure.
In an effort to address the problem of gaping, oil filled bags and pads have been used to fill the void in the gaps. But when such bags and pads are used in the glove of a suit, fluid accumulation has only been reduced, not eliminated. Perhaps more importantly, the bags/pads significantly impede dexterity. Also, as the need for more counterpressure increases, so does the need for a bag/pad which is larger and/or nonpliable. However, as the bag/pad increases in size and/or stiffness, dexterity decreases. Additionally, increased size and stiffness makes donning and doffing more difficult.
As can be seen, there is a need for an improved counterpressure garment for low pressure environments, such as outer space. Also needed is an improved counterpressure garment that can provide a counterpressure of about 222 mm Hg. A further need is for a garment that can provide counterpressure to blood supplied tissue that is significantly noncircular in shape and subject to frequent contraction, such as a human hand. Another need is for a space suit glove that not only provides adequate counterpressure to the palm and fingers of a hand but is also relatively easy to don and doff. Yet another need is for a method of equalizing a breathing pressure and tissue pressure in the palm of a hand. Such a space suit glove may be part of a complete SAS garment, or it might be used as the glove with a full pressure suit, or as the glove of a partial pressure suit.